1. Field of the Invention
This invention relates to a printing die replacement assisting unit in a printing apparatus for applying a predetermined print on corrugated board sheets, in which the printing die mounted around the plate cylinder can easily be replaced.
2. Description of the Related Art
The printing apparatus which applies a print on corrugate board sheets cut into a predetermined length is provided with a plate cylinder and an impression cylinder arranged in a vertical relationship, i.e. at an upper position and a lower position with respect to the corrugated board sheet pass line, and a desired printing die is designed to be removably mounted around the plate cylinder. An ink is transferred to the printing die with the aid of an ink transfer mechanism disposed above the plate cylinder, and a corrugated board sheet is passed between the plate cylinder and the impression cylinder to apply a required print on the sheet.
An engagement groove and a clamping groove are formed on the circumference of the plate cylinder parallelwise in the axial direction, with a clamp being disposed in the clamping groove. When the printing die is to be mounted on the circumference of the plate cylinder, one of the engagement plates disposed at the end portions of the printing die relative to the die rolling direction is engaged in the engagement groove, and the plate cylinder is then turned to roll the printing die therearound. After the printing die is substantially rolled around the plate cylinder, the other engagement plate of the printing die is clamped and tightened by the clamp disposed in the clamping groove, whereby the printing die can be mounted on the circumference of the plate cylinder.
In such printing apparatus, when the printing die (old printing die) mounted around the plate cylinder is to be replaced in accordance with an order change with another printing die (new printing die) of the next order, an operator first releases the old printing die mounted around the plate cylinder and lays it on the floor or somewhere else. After the operator puts one engagement plate of the new printing die in the engagement groove of the plate cylinder, he holds the free end portion of the new printing die and turns the plate cylinder, whereby the new printing die is rolled around the plate cylinder. After the other engagement plate of the new printing die is clamped by the clamp disposed in the clamping groove, the new printing die is tightened by the clamp to complete the replacement operation.
In this case, when the printing die, one engagement plate thereof being caught in the engagement groove of the plate cylinder, is to be mounted around the plate cylinder, it is not so difficult for one operator to hold the free end portion of the printing die, so long as the width of the printing plate (length in the axial direction of the plate cylinder) is small. However, if the printing die is wide, it is too tough for one operator to hold such heavy printing die so as to cope with such operation, forcing overburden on the operator and reducing operation efficiency, disadvantageously. Thus, in carrying out replacement of a wide printing die, the free end portion of the printing die is generally held by two operators on each side of the printing die. However, increase in the labor cost can be pointed out in this case. Besides, the old printing die released from the plate cylinder must be placed on the floor on which a new printing die has already been provided, so that the floor is occupied by two printing dies to interfere with the replacing operation, disadvantageously.
In order to overcome such problems, Japanese Unexamined Patent Publication Nos. 133069/1982 and 133070/1982 disclose systems. In these systems, a printing die replacing unit is disposed adjacent to the printing apparatus so as to carry out removal of the old printing die from the plate cylinder and mounting of the new printing die therearound automatically in accordance with order changes.
However, it can be pointed out that a complicated mechanism must be employed in these systems, leading to cost elevation, disadvantageously. In addition, a space must be secured for installing the large replacing unit, so that the space in the factory cannot effectively be utilized. Moreover, it can also be pointed out, in order to cope with the automation of printing die replacement with the aid of the printing die replacing unit, that special working must be applied to the printing dies and the plate cylinder, that special jigs must be provided, and that the facility investment for the automation jumps up, disadvantageously. Accordingly, such systems can hardly be utilized in actual applications.